Mobile communication systems have been developed to provide voice services while ensuring the activity of a user. However, the mobile communication systems have been expanded to their regions up to data services as well as voice. Today, the shortage of resources is caused due to an explosive increase of traffic, and more advanced mobile communication systems are required due to user's need for higher speed services.
Requirements for a next-generation mobile communication system basically include the acceptance of explosive data traffic, a significant increase of a transfer rate per user, the acceptance of the number of significantly increased connection devices, very low end-to-end latency, and high energy efficiency. To this end, research is carried out on various technologies, such as dual connectivity, massive Multiple Input Multiple Output (MIMO), in-band full duplex, Non-Orthogonal Multiple Access (NOMA), the support of a super wideband, and device networking.
Direction communication between devices, that is, device-to-device (D2D) communication, refers to a communication method for setting up a direct link between a plurality of devices (e.g., a plurality of types of user equipments (UE) and directly exchanging voice and data between the plurality of devices without the intervention of an evolved NodeB (eNB).
D2D communication may include methods, such as UE-to-UE communication and peer-to-peer communication. Furthermore, the D2D communication method may be applied to machine-to-machine (M2M) communication and machine type communication (MTC).
D2D communication has been taken into consideration as one of methods capable of solving the burden of an eNB attributable to data traffic that is suddenly increased. For example, in accordance with D2D communication, overhead of a network can be reduced because data can be exchanged between devices without the intervention of an eNB unlike in an existing wireless communication system.
Furthermore, if D2D communication is adopted, effects, such as a reduction of some of the procedures of an eNB, a reduction of power consumed by devices participating in D2D, an increase of a data transfer rate, an increase of the accommodation ability of a network, a load distribution, and the expansion of cell coverage, can be expected.